1. Technical Field
The present invention relates generally to battery-powered electronic devices and, more particularly, to a method of calibrating capacities of rechargeable batteries.
2. Related Art
Rechargeable batteries are presently used in many portable electronic devices, such as computers, camcorders, and mobile phones. Such devices are also capable of utilizing alternating current (AC) power. Battery power is utilized when AC power is not convenient or is not available.
Various types of rechargeable batteries are known to be used in such applications. For example, nickel-cadmium (NiCad), nickel metal hydride (NiMH), and lithium ion batteries are used.
Typically, a portable computer system is powered by either a smart rechargeable battery pack or by alternating current (AC) through an AC-to-DC adapter. Such smart batteries typically include memory storage devices, and some smart battery packs include a microcontroller.
With respect to the smart batteries, it is important to provide accurate information regarding the remaining capacities of the batteries. Some smart batteries incorporate "fuel gauge" functions, by which the charge levels of the batteries can be indicated. An example of rechargeable batteries with such fuel gauge functions is described in U.S. Pat. No. 5,315,228. Typically, a rechargeable battery measures its discharge current, estimates its self-discharge, and predicts its remaining capacity.
In most portable computers, a power management system's prediction of run time remaining and a user's actual run time do not correspond. This disparity may increase when usage patterns vary widely.
The typical fuel gauge approach simply uses a recent value for average current consumption to calculate the remaining run time of the system. This may provide inaccurate information as to the remaining capacity of the battery. If, for example, the remaining run time of the system reported from the fuel gauge is shorter than its actual run time, then the user cannot consume its full battery capacity. Conversely, if the remaining run time of the system reported from the fuel gauge is longer than its actual run time, the portable computer system will be shut down before the calculated run time.
One solution to the foregoing problem is to correct the graduations of the battery capacity, which is usually called "battery calibration". Prior to calibration, a battery must be fully charged. The fully charged battery is fully discharged for an exact learning of the battery capacity. However, the calibration of a battery takes a long time (i.e., about 2-3 hours) because of its long discharge time. Considering total time of the calibrating process, the discharging process occupies the majority of the total time. In order to reduce the calibration time of a battery, its faster discharge is demanded.
The following patents are considered to be representative of the prior art relative to the invention disclosed herein, but are burdened by the disadvantages set forth above:
U.S. Pat. No. 4,151,454 for Remaining Capacity Detector of a Battery issued to Iida; U.S. Pat. No. 3,969,667 for Device for Determining the State of Charge in Batteries issued to McWilliams; U.S. Pat. No. 4,207,611 for Apparatus and Method for Calibrated Testing of a Vehicle Electrical System issued to Gordon; U.S. Pat. No. 4,290,002 for Method and Apparatus for Controlling Battery Recharging issued to Piotti; U.S. Pat. No. 4,912,392 for Battery Charge State Monitor issued to Faulkner; U.S. Pat. No. 5,140,269 for Electronic Tester for Assessing Battery/Cell Capacity issued to Champlin; U.S. Pat. No. 5,268,845 for Method for Detecting Low Battery State Without Precise Calibration issued to Startup et al.; U.S. Pat. No. 5.363,689 for Calibration Device for Leak Detecting Instruments issued to Hoffmann et al.; U.S. Pat. No. 5,472,056 for Control System for Agricultural Vehicle and Calibration Method for Such Control Systems issued to Orbach; U.S. Pat. No. 5,563,496 for Battery Monitoring and Charging Control Unit issued to McClure; and U.S. Pat. No. 5,596,260 for Apparatus and Method for Determining a Charge of a Battery issued to Moravec et al.